Subject: Re: [PATCH v3 1/2] iio: adc: mt6360: Add ADC driver for MT6360

From: Jonathan Cameron <[email-masked]>
Date: Tue, 8 Sep 2020 13:58:30 +0100

...

> > > > > +#include <linux/completion.h>
> > > > > +#include <linux/interrupt.h>
> > > > > +#include <linux/iio/buffer.h>
> > > > > +#include <linux/iio/iio.h>
> > > > > +#include <linux/iio/trigger_consumer.h>
> > > > > +#include <linux/iio/triggered_buffer.h>
> > > > > +#include <linux/irq.h>
> > > > > +#include <linux/kernel.h>
> > > > > +#include <linux/ktime.h>
> > > > > +#include <linux/module.h>
> > > > > +#include <linux/mutex.h>
> > > > > +#include <linux/platform_device.h>
> > > > > +#include <linux/regmap.h>
> > > > > +
> > > > > +#define MT6360_REG_PMUCHGCTRL3       0x313
> > > > > +#define MT6360_REG_PMUADCCFG 0x356
> > > > > +#define MT6360_REG_PMUADCRPT1        0x35A
> > > > > +
> > > > > +/* PMUCHGCTRL3 0x313 */
> > > > > +#define MT6360_AICR_MASK     0xFC
> > > > > +#define MT6360_AICR_SHFT     2
> > > > > +#define MT6360_AICR_400MA    0x6
> > > > > +/* PMUADCCFG 0x356 */
> > > > > +#define MT6360_ADCEN_MASK    0x8000
> > > > > +/* PMUADCRPT1 0x35A */
> > > > > +#define MT6360_PREFERCH_MASK 0xF0
> > > > > +#define MT6360_PREFERCH_SHFT 4
> > > > > +#define MT6360_RPTCH_MASK    0x0F
> > > > > +
> > > > > +enum {
> > > > > +     MT6360_CHAN_USBID = 0,
> > > > > +     MT6360_CHAN_VBUSDIV5,
> > > > > +     MT6360_CHAN_VBUSDIV2,
> > > > > +     MT6360_CHAN_VSYS,
> > > > > +     MT6360_CHAN_VBAT,
> > > > > +     MT6360_CHAN_IBUS,
> > > > > +     MT6360_CHAN_IBAT,
> > > > > +     MT6360_CHAN_CHG_VDDP,
> > > > > +     MT6360_CHAN_TEMP_JC,
> > > > > +     MT6360_CHAN_VREF_TS,
> > > > > +     MT6360_CHAN_TS,
> > > > > +     MT6360_CHAN_MAX,
> > > > > +};
> > > > > +
> > > > > +struct mt6360_adc_data {
> > > > > +     struct device *dev;
> > > > > +     struct regmap *regmap;
> > > > > +     struct completion adc_complete;
> > > > > +     struct mutex adc_lock;
> > > > > +     ktime_t last_off_timestamps[MT6360_CHAN_MAX];
> > > > > +     int irq;
> > > > > +};
> > > > > +
> > > > > +static inline int mt6360_adc_val_converter(int val, int multiplier, int offset, int divisor)
> > > > > +{
> > > > > +     return ((val * multiplier) + offset) / divisor;  
> > > >
> > > > Why could we not report these values to userspace or consumer drivers and let
> > > > them deal with the conversion if they actually needed it?
> > > > Mapping this to
> > > >
> > > > (val + new_offset) * multiplier would be a little messy, but not too bad.
> > > >
> > > > The advantage would be that we would then be providing the data needed
> > > > to get real units for values read from the buffers without having to
> > > > do all the maths in kernel (without access to floating point).
> > > >
> > > >  
> > >
> > > As above, if I use formula "(val + new_offset) * multiplier",
> > > the junction temperature channel multiplier will be floating point
> > > 1.05, i don't know how to express.  
> >
> > As Andy mentioned, we do this all over the place.
> > IIO_VAL_INT_PLUS_MICRO
> >
> > The key is that we want to push the burden of doing this maths to the user
> > not the source.  
> 
> ACK.
> Can I keep IIO_CHAN_INFO_PROCESSED function be reserved for user in
> kernel space?
> 

No. We have utility functions that will apply the multiplier as needed so
there is no significant advantage in doing this and it won't be consistent
with the majority of other drivers. 

> >
> > Often what is actually of interest is whether a temperature passed a threshold.
> > In that case, you can transform the threshold into the units of the ADC (so the
> > reverse directly to you would do with processed data) and only have to do the
> > maths once per change of the threshold instead of for every sample.
> >
> > There are helper functions to do the maths for you, should you actually
> > need SI units.
> >  
> 
> ACK
> 
> > >  
> > > > > +}
> > > > > +
> > > > > +static int mt6360_adc_convert_processed_val(struct mt6360_adc_data *info, int chan_idx, int *val)
> > > > > +{
> > > > > +     unsigned int regval = 0;
> > > > > +     const struct converter {
> > > > > +             int multiplier;
> > > > > +             int offset;
> > > > > +             int divisor;
> > > > > +     } adc_converter[MT6360_CHAN_MAX] = {
> > > > > +             { 1250, 0, 1}, /* USBID */
> > > > > +             { 6250, 0, 1}, /* VBUSDIV5 */
> > > > > +             { 2500, 0, 1}, /* VBUSDIV2 */
> > > > > +             { 1250, 0, 1}, /* VSYS */
> > > > > +             { 1250, 0, 1}, /* VBAT */
> > > > > +             { 2500, 0, 1}, /* IBUS */
> > > > > +             { 2500, 0, 1}, /* IBAT */
> > > > > +             { 1250, 0, 1}, /* CHG_VDDP */
> > > > > +             { 105, -8000, 100}, /* TEMP_JC */
> > > > > +             { 1250, 0, 1}, /* VREF_TS */
> > > > > +             { 1250, 0, 1}, /* TS */
> > > > > +     }, sp_ibus_adc_converter = { 1900, 0, 1 }, *sel_converter;
> > > > > +     int ret;
> > > > > +
> > > > > +     sel_converter = adc_converter + chan_idx;
> > > > > +     if (chan_idx == MT6360_CHAN_IBUS) {
> > > > > +             /* ibus chan will be affected by aicr config */
> > > > > +             /* if aicr < 400, apply the special ibus converter */
> > > > > +             ret = regmap_read(info->regmap, MT6360_REG_PMUCHGCTRL3, &regval);
> > > > > +             if (ret)
> > > > > +                     return ret;
> > > > > +
> > > > > +             regval = (regval & MT6360_AICR_MASK) >> MT6360_AICR_SHFT;
> > > > > +             if (regval < MT6360_AICR_400MA)
> > > > > +                     sel_converter = &sp_ibus_adc_converter;
> > > > > +     }
> > > > > +
> > > > > +     *val = mt6360_adc_val_converter(*val, sel_converter->multiplier, sel_converter->offset,
> > > > > +                                     sel_converter->divisor);
> > > > > +
> > > > > +     return 0;
> > > > > +}
> > > > > +
> > > > > +static int mt6360_adc_read_processed(struct mt6360_adc_data *mad, int channel, int *val)
> > > > > +{
> > > > > +     u16 adc_enable;
> > > > > +     u8 rpt[3];
> > > > > +     ktime_t start_t, predict_end_t;
> > > > > +     long timeout;
> > > > > +     int value, ret;
> > > > > +
> > > > > +     mutex_lock(&mad->adc_lock);
> > > > > +
> > > > > +     /* select preferred channel that we want */
> > > > > +     ret = regmap_update_bits(mad->regmap, MT6360_REG_PMUADCRPT1, MT6360_PREFERCH_MASK,
> > > > > +                              channel << MT6360_PREFERCH_SHFT);
> > > > > +     if (ret)
> > > > > +             goto out_adc;
> > > > > +
> > > > > +     /* enable adc channel we want and adc_en */
> > > > > +     adc_enable = MT6360_ADCEN_MASK | BIT(channel);
> > > > > +     adc_enable = cpu_to_be16(adc_enable);  
> > > >
> > > > Use a local be16 to store that. It will make it a little clearer
> > > > that we are doing something 'unusual' here.  Perhaps a comment on
> > > > why this odd code exists would also help?
> > > >  
> > >
> > > ACK
> > >  
> > > > > +     ret = regmap_raw_write(mad->regmap, MT6360_REG_PMUADCCFG, (void *)&adc_enable, sizeof(u16));
> > > > > +     if (ret)
> > > > > +             goto out_adc;
> > > > > +
> > > > > +     start_t = ktime_get();
> > > > > +     predict_end_t = ktime_add_ms(mad->last_off_timestamps[channel], 50);
> > > > > +
> > > > > +     if (ktime_after(start_t, predict_end_t))
> > > > > +             predict_end_t = ktime_add_ms(start_t, 25);
> > > > > +     else
> > > > > +             predict_end_t = ktime_add_ms(start_t, 75);
> > > > > +
> > > > > +     enable_irq(mad->irq);
> > > > > +adc_retry:
> > > > > +     reinit_completion(&mad->adc_complete);
> > > > > +
> > > > > +     /* wait for conversion to complete */
> > > > > +     timeout = wait_for_completion_timeout(&mad->adc_complete, msecs_to_jiffies(200));
> > > > > +     if (timeout == 0) {
> > > > > +             ret = -ETIMEDOUT;
> > > > > +             goto out_adc_conv;
> > > > > +     } else if (timeout < 0) {
> > > > > +             ret = -EINTR;
> > > > > +             goto out_adc_conv;
> > > > > +     }
> > > > > +
> > > > > +     ret = regmap_raw_read(mad->regmap, MT6360_REG_PMUADCRPT1, rpt, sizeof(rpt));
> > > > > +     if (ret)
> > > > > +             goto out_adc_conv;
> > > > > +
> > > > > +     /* check the current reported channel */
> > > > > +     if ((rpt[0] & MT6360_RPTCH_MASK) != channel) {
> > > > > +             dev_dbg(mad->dev, "not wanted channel report [%02x]\n", rpt[0]);  
> > > >
> > > > This and the one below feel like error messages rather than debug ones.
> > > >  
> > >
> > > We have two function "battery zero current voltage(ZCV)" and "TypeC
> > > OTP" will auto run ADC at background.
> > > ZCV_EN will run VBAT_ADC when TA plug in, TypeC OTP will run TS_ADC
> > > when TypeC attach.
> > > We need to check report channel for ADC report data match is our desire channel.  
> >
> > So there is firmware messing with it underneath?  Oh goody.
> > Add a comment explaining this.
> >  
> 
> ACK, I try to write a comment as below
> 
>         /*
>          * There are two functions, ZCV and TypeC OTP, running ADC
> VBAT and TS in background,
>          * and ADC samples are taken on a fixed frequency no matter
> read the previous one or not.
>          * To avoid conflict need set minimum time threshold after
> enable ADC and check report
>          * channel is the same.
>          * The worst case is run the same ADC twice and background
> function is also running,
>          * ADC conversion sequence is desire channel before start ADC,
> background ADC, desire
>          * channel after start ADC. So the minimum correct data is
> three times of typical
>          * conversion time.
>          */

Looks good.

> 
> > >  
> > > > > +             goto adc_retry;
> > > > > +     }
> > > > > +
> > > > > +     if (!ktime_after(ktime_get(), predict_end_t)) {
> > > > > +             dev_dbg(mad->dev, "time is not after one adc_conv_t\n");  
> > > >
> > > > Does this actually happen? If feels like we are being a bit over protective
> > > > here.  I'd definitely like to see a comment saying why this protection
> > > > might be needed.
> > > >  
> > >
> > > When ADC_EN and MT6360_CHANx_EN is enable, the channel x will keep
> > > running again and again
> > > I supposed to get immediate data which is generated after I start it.  
> >
> > Just to check my understanding.
> >
> > This is an edge triggered interrupt and it triggers every time a new sample
> > is taken.  Those samples are taken on a fixed frequency irrespective of whether
> > we have read the previous one?
> >  
> 
> Yes.
> I use LEVEL_LOW trigger in latest review MFD patch.

I'm not sure I follow that comment.  How can you do that if it's a repeating
edge trigger? 

> 
> > >
> > > When I disable ADC_CHANx_EN, the H/W logical ADC is still running.
> > > If I run the same ADC immediately, I may get the old result about this channel.
> > > MT6360 ADC typical conversation time is about 25ms.
> > > So We need ignore which irq trigger below 25ms.  
> >
> > Normal trick for this sort of case is to just not use the interrupt.
> > Just read after 25+delta msecs and you are guaranteed to get the right answer.
> >
> >  
> 
> ACK, I will try to use polling
> Is the pseudocode correct?
> 
> mdelay(predict_end_t);
> while (true) {
>     read adc event is occured
>     check report channel is the same
>     if the same, read report ADC data and break while loop
>     else msleep(per ADC conversion time)
> }

Looks correct to me.  We should 'know' the event has happened but
still need to check the channel is the expected one.

...

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